1. Field of the Invention
The present invention relates to a time keeping apparatus and a control method for it, more particularly to a radio-controlled timepiece having a power saving function to reduce its power consumption.
2. Description of the Related Art
A radio-controlled watch that has a power saving function and receives time data from the outside and adjusts the time is disclosed in Japanese Patent Application Laid Open Publication No. 11-223684 entitled “radio-controlled watch”. The radio-controlled watch has a thermoelectric generator that generates electricity by using temperature difference between the wearer's arm and outside air. The watch stores the electricity in its storage unit and uses the electricity to operate.
The radio-controlled watch periodically receives a standard time radio signal by the Communications Research Laboratory (CRL) of Japan that is transmitted at a frequency of 40 kHz under a call sign of JJY (its former call sign was JG2AS). In the radio wave, time data is superimposed, and one set of the time data has a length of 60 seconds. The time data has data of current hour, current minute, and current day which shows the number of days from January first of that year. Based on the time data, the time of the watch is adjusted.
However, the radio-controlled watch has a problem. The problem is that when a user wears the watch that is left unused for a long time, the user cannot know the correct time for several minutes. This is because the time adjustment of the watch is conducted only after the watch receives several sets of the time data. This is also because there are cases where the watch does not conduct a time adjustment, but continues to perform a time display: one case of them is when the battery voltage declines below a certain voltage where time display can become incorrect.